The incidence of Hib before vaccination began was 30/100,000 among whites, and 600/100,000 among Aboriginal people in Alaska. The incidence in the United States increased 4-fold from 1940 to 1970. The same happened in Scotland and Sweden.Breastfeeding has a protective effect against meningitis caused by Hib, and this effect lasts 5-10 years.A short period of breastfeeding (less than 13 weeks) increases the risk of Hib 3.79 times. Painful children get sick 4.5 times more often.Breast milk has an inhibitory effect on the attachment of bacteria to the mucous membrane of the nasopharynx.As the chart shows, after the decrease in the number of children on breastfeeding, the incidence of Hib increased, and when their percentage increased again, the incidence of Hib decreased.

Among children over 1 year of age, a short period of breastfeeding (HS) is associated with an increased risk of Hib 7.79-fold. Each additional week of HB reduced the risk of Hib by 5%. The protective effect of HB started already with 13 weeks of exclusive breastfeeding, and lasted for months and years.

Among children under 6 months of age, exclusive HB is associated with a 90% reduction in Hib risk. Visiting kindergarten - increasing the risk by 1.9-5.9 times. The larger the group in the garden, the higher the risk.

In Sweden and Finland, there has been no increase in the number of cases of Hib after switching to acellular pertussis vaccine, the authors believe that this is due to the fact that longer breastfeeding is common in these countries.

The protective level of antibodies of diphtheria is considered to be from 0.01 to 0.1 IU/ml. The exact value cannot be determined.

Not a single case of diphtheria has been recorded in Sweden from the late 1950s to 1984. 3 outbreaks were observed in 1984 (17 cases, 3 deaths). Almost all patients were chronic alcoholics. Most patients had the level of antibodies below 0.01 IU/ml.

Researchers measured the level of antibodies in children. 48% of those who received 3 doses of the vaccine in infancy had the antibodies level below 0.01 IU/ml. Among the 6-year-olds 15% had such results. Among the 16-year-olds, who have received booster vaccines in addition to being vaccinated in infancy, 24% had the antibodies level below 0.01 IU/ml. It is possible that the low level of antibodies in Sweden could be due to the fact that the whooping cough component has been excluded from the vaccine in the 1970s. Since the whooping cough toxin is an adjuvant itself, its exclusion makes the diphtheria vaccine less effective.

The immune response to booster vaccines among 16-year-olds was much worse than that of 6-year-olds, even despite the fact that 16-year-olds received a 2.5 times bigger doses. The authors do not have an explanation for this phenomenon.

It is believed that antibodies level above 1 IU/ml provides protection for over 10 years. Only 50% of 16-year-olds and 22% of 10-year-olds had such level of antibodies after vaccination.

The level of antibodies falls by 20-30% in a year. It decreases even faster in children. While 94% of children at the age of 15 months had the level of antibodies above 1 IU/ml, 4 years later the average level of for them was only 0.062 IU/ml.

The authors measured antibodies level of 2,400 people in Sweden. 19% of people of the age of 20 and under did not have immunity against diphtheria. Among people over 40 years of age, only 15% had sufficient level of antibodies. Among the elderly, 81% of women and 56% of men did not have the immunity. On average, 70% of adult women and 50% of adult men had antibodies level below 0.01 IU/ml.

After 1978, it was discovered that 84% of pertussis patients had been vaccinated with three doses of the vaccine. Consequently, in 1979 Sweden stopped administering the vaccination. Only in 1996, when the acellular vaccine appeared, was vaccination reinstated.

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